The present invention relates to a dust boot for a universal joint which is used in a drive system for an automobile.
In most cases, the universal joint is covered with a dust boot for protecting the universal joint from dust and water and for retaining lubricating oil. The dust boot is generally made of rubber or synthetic resin having resilience and flexibility. Each open end of the dust boot is closely fixed to each outer periphery of a first and a second joint elements of the universal joints. The dust boot covers the coupling portion of both joint elements by a covering portion thereof having a deformable shape such as bellows.
The first and second joint elements are generally a driving shaft and a driven shaft. An end of the second joint element is connected to a housing. Within the housing, an end of the other joint element is positioned and connected thereto so that the angular relation between joint elements can be freely changed.
One open end of the dust boot is closely mounted on the outer peripheral surface of the universal joint housing and the other end thereof is closely mounted on the outer peripheral surface of the shaft of the first joint element which is connected to the housing.
The outer peripheral surface of the housing can be formed into various shapes according to the coupling structure within the housing.
FIG. 1 shows one example of the shape of the outer peripheral surface of the housing. The outer peripheral surface of the housing which is shown by a rigid line a is composed of straight portions a.sub.1, curved portions a.sub.2 and corner portions a.sub.3 which connect portions a.sub.1 and a.sub.2. The housing shapes an inflated triangle as a whole. And each of the corner portions a.sub.3 has especially larger curvature than that of the other portions.
In general, a difference exists between the cross-sectional area; an open end of the dust boot made of resilient material and the outer peripheral surface of the housing on which the dust boot is mounted, for obtaining a strong clamping force.
The area of the end opening of the dust boot is formed smaller than the cross-sectional area of the outer peripheral surface of the housing.
However, when the open end of the dust boot is mounted on the housing having such a shape as described above, slippage often occurs therebetween so that the corner portions a.sub.3 of the housing do not precisely face to the corner portions of the open end of the dust boot.
In such a case, in the corner portions a.sub.3 of the housing, there occurs a gap between the housing and the open end of the dust boot so that the dust boot cannot sufficiently achieve a sealing effect.
The outer peripheral surface of the open end of the dust boot which is closely mounted on the housing is clamped by a ring, in general. However, in order to completely seal the universal joint and prevent the gap occurring in the corner portion a.sub.3, a high clamping load is necessary. But such a high clamping load as is required for completely sealing the gap cannot be obtained by a hand work.
In order to improve the sealing effect, the open ends of the dust boot can be made deformable (for example, thin) and to make the interference larger. But, according to these methods, the ends of the dust boot are buckled so as to be easily damaged. And if the interference of the dust boot is made larger, it becomes difficult to closely mount the dust boot on the housing.
Accordingly, one object of the present invention is to provide a dust boot for covering a coupling portion of a universal joint composed of two joint elements, at least one of which has an outer peripheral surface having a changing curvature.
Another object of the present invention is to provide a dust boot which is easily mounted on the joint elements of the universal joint with excellent sealing effect.